How to retrieve dictionary key when knowing value on one of its attributes?

Question

Recently I was working on my Netbox automation using Ansible. I prepared task, which collects information about network interfaces that looks like below:

"interface_ips": {
  "br0": {
    "ipv4": [                
      "10.0.0.10",
      "10.0.0.11"
    ],
    "ipv6": [],
    "mac": "aa:bb:cc:dd:ee:ff",
    "mtu": "1500",
    "type": "bridge"
  },
  "lxcbr0": {
    "ipv4": [
      "10.100.0.10"
    ],
    "ipv6": [],
    "mac": "ff:ee:dd:cc:bb:aa",
    "mtu": "1500",
    "type": "bridge"
  }
}

I wanted to iterate over collected IPs (IPv4 + IPv6) and return interface name for corresponding IP.

The output I want is the following:

• 10.0.0.10 - br0 - host
• 10.0.0.11 - br0 - host
• 10.100.0.10 - lxcbr0 - host

Some interfaces might have multiple IPs assigned, so it's very important to iterate over every IP.

I managed to do following task, but it doesn't iterate over every address, only first ipv4 address.

- name: Extract IPv4 addresses and interface names
  set_fact:
    ip_interface_map: "{{ ip_interface_map | default({}) | combine({item.value.ipv4[0]: item.key}) }}"
    loop: "{{ interface_ips | dict2items }}"

Can this be done easily somehow?

Answer 1

Convert the dictionary to a list

  interface_ips | dict2items:
    - key: br0
      value:
        ipv4: [10.0.0.10, 10.0.0.11]
        ipv6: []
        mac: aa:bb:cc:dd:ee:ff
        mtu: '1500'
        type: bridge
    - key: lxcbr0
      value:
        ipv4: [10.100.0.10]
        ipv6: []
        mac: ff:ee:dd:cc:bb:aa
        mtu: '1500'
        type: bridge

---

• Iterate subelements

  - debug:
      msg: "{{ item.1 }} - {{ item.0.key }}"
    loop: "{{ interface_ips | dict2items | subelements('value.ipv4') }}"

gives (abridged)

  msg: 10.0.0.10 - br0
  msg: 10.0.0.11 - br0
  msg: 10.100.0.10 - lxcbr0

The same loop with subelements('value.ipv6') will be skipped because all ipv6 lists are empty

  - debug:
      msg: "{{ item.1 }} - {{ item.0.key }}"
    loop: "{{ interface_ips | dict2items | subelements('value.ipv6') }}"

• Optionally, create a dictionary first

  ip_interface_map: "{{ dict(interface_ips | dict2items | 
                             json_query('[].[key, 
                                            [value.ipv4, value.ipv6]|[]]')) }}"

gives

  ip_interface_map:
    br0:
    - 10.0.0.10
    - 10.0.0.11
    lxcbr0:
    - 10.100.0.10

• Iterate subelements

  - debug:
      msg: "{{ item.1 }} - {{ item.0.key }}"
    loop: "{{ ip_interface_map | dict2items | subelements('value') }}"

gives (abridged) the same result

  msg: 10.0.0.10 - br0
  msg: 10.0.0.11 - br0
  msg: 10.100.0.10 - lxcbr0

---

Example of a complete playbook for testing

- hosts: all

  vars:

    interface_ips:
      br0:
        ipv4: [10.0.0.10, 10.0.0.11]
        ipv6: []
        mac: aa:bb:cc:dd:ee:ff
        mtu: '1500'
        type: bridge
      lxcbr0:
        ipv4: [10.100.0.10]
        ipv6: []
        mac: ff:ee:dd:cc:bb:aa
        mtu: '1500'
        type: bridge

    ip_interface_map: "{{ dict(interface_ips | dict2items |
                               json_query('[].[key,
                                              [value.ipv4, value.ipv6]|[]]')) }}"

  tasks:

    - debug:
        msg: "{{ item.1 }} - {{ item.0.key }}"
      loop: "{{ interface_ips | dict2items | subelements('value.ipv4') }}"
    - debug:
        msg: "{{ item.1 }} - {{ item.0.key }}"
      loop: "{{ interface_ips | dict2items | subelements('value.ipv6') }}"

    - debug:
        var: ip_interface_map

    - debug:
        msg: "{{ item.1 }} - {{ item.0.key }}"
      loop: "{{ ip_interface_map | dict2items | subelements('value') }}"